A serous membrane is a very thin layer of cells (usually one row) covering internal body cavity. The cells constituting this membrane secrete a so called serous fluid to the membrane's surface, which keeps the membrane moistened. This article or section should include material from Net flux A membrane is a thin, typically planar structure or material that separates two environments. ... A cell is a single unit or compartment, enclosed by a border or wall. ... This article or section should include material from Net flux A membrane is a thin, typically planar structure or material that separates two environments. ...